Cleaning sheets made from paper, nonwoven fabrics and the like are used to wipe human skin on the buttocks, for example, or to clean toilet areas. Such cleaning sheets must have a certain degree of water disintegratability so that they can be flushed through the toilet for disposal after use. This is because when a low-water disintegratable cleaning sheet or the like is flushed and disposed of through the toilet, it can potentially clog waste water pipes or require greater time for dispersing in clarification tanks.
The cleaning sheets described above are also often packaged and sold in pre-moistened form with cleaning chemicals and the like, from the viewpoint of convenience and working efficiency. Such cleaning sheets must therefore have sufficient wet strength in order to withstand removal and wiping operations in a moistened state produced by impregnation with cleaning chemicals or the like.
In other words, such cleaning sheets must have water disintegratability and wet strength properties that at first appear to be incompatible.
In order to solve this problem, PTL1, for example, discloses a water disintegratable cleaning article comprising a carboxyl group-containing water-soluble binder, a metal ion and an organic solvent. However, safety is an issue because of the skin irritability of the metal ion and organic solvent used in the water disintegratable cleaning article.
PTL2 discloses a water disintegratable cleaning article obtained by impregnating polyvinyl alcohol-containing fibers with a boric acid aqueous solution. However, polyvinyl alcohol is poorly heat-resistant, and the wet strength of the water disintegratable cleaning article is reduced at above 40° C.
PTL3, on the other hand, discloses a water-collapsible nonwoven fabric with a wet strength of 100-800 gf/25 mm as measured according to JIS P 8135, which is obtained by tangling with high-pressure water jet flow treatment following blending of pulp with fiber having an average fiber length of 4-20 mm. The fabric has a high-bulk feel since it is a nonwoven fabric with entangled fibers. However, because fibers with a long average fiber length become entangled by high-pressure water jet treatment, resulting in relatively high wet strength in the nonwoven fabric, it has been difficult to achieve both strength and water disintegratability.
In order to solve the problems described above, the present applicants have previously disclosed, in PTL4 and PTL5, water disintegratable fibrous sheets containing fibrillated rayon composed of main bodies with prescribed fiber lengths and microfibers that extend from the main bodies. The water disintegratable fibrous sheets exhibit both a certain degree of water disintegratability and wet strength, but the technical field has a demand for water disintegratable fibrous sheets with even higher wet strength and/or water disintegratability.